This application claims the benefit of British Application No. 0012994.0, filed May 26, 2000, in the British Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an article handling system comprising a flow path along which articles travel and a metal detection system to detect the passage of metal items along the flow path. The invention also relates to a method to monitor the performance of a metal detection system.
2. Description of the Related Art
Metal detection systems are used in a wide range of article handling systems to monitor the presence of metal items, particularly those for handling foodstuffs. If a metal item is detected, the system must be stopped to enable the item to be extracted.
It is important to check the sensitivity and performance of the metal detection system. In conventional weighing systems in which articles such as potato chips are dropped generally vertically from a weighing machine to a packaging machine, the sensitivity of the metal detection system provided around the flow path is checked by dropping a metal test piece along the flow path. Conventionally, this has been done by manually dropping the test piece, which may be an iron or a stainless steel sphere, and determining whether or not the metal detection system senses the passage of the item. This is then repeated with spheres of different sizes. In view of the need to introduce the metal test piece into the flow path, it is conventional to stop the article handling system while the sensitivity check is carried out.
There are a number of problems with the conventional systems. One of the most significant is the need to recover the test piece after the test. This is often difficult to achieve and will result in significant waste of bags and the like while the test piece is located. It is therefore important to monitor the output from the article handling system to ensure that the metal piece can be retrieved.
Furthermore, particularly in the case of combination weighing machines, since the metal test piece is dropped through a relatively narrow opening, there is a risk that the test piece may be caught in the machine and will require significant time to be recovered. It is also important that the test piece passes a predetermined position to ensure that the sensitivity of the metal detection system is correctly adjusted. This is difficult to achieve with the conventional systems.
U.S. Pat. No. 4,726,434 describes a method of checking the sensitivity of a metal detection system provided around a discharge chute of a combination weighing machine. A metal test piece is supplied to one of the weighers of a combination weighing machine and the processor ensures that at the correct time, this particular weigher is involved in the combination which is released. Nevertheless, it is still necessary to recover the test piece and to stop the weighing machine following the test cycle.
Accordingly, it is an object of the present invention to provide an article handling system that overcomes the above disadvantages of the prior system. Additional objects and advantages will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.
The foregoing objects of the present invention are achieved by providing an article handling system comprising a flow path along which articles travel and a metal detection system having a metal detector to detect the passage of metal items along the flow path. A metal detector test system supporting a metal test piece is located relative to the flow path to move the test piece along the flow path past the metal detector in order to detect the sensitivity of the detector.
The foregoing objects may also be achieved with a method to monitor the performance of a metal detection system having a metal detector to detect the passage of metal items along a flow path of an article handling system that comprises controllably moving a metal test piece along the flow path and determining whether the metal detection system detects the metal test piece.
Unlike the known arrangements, the present metal detector test system supports the metal test piece and positively moves it along the flow path. The problem of recovery is eliminated since the metal test piece remains supported by the test system while the test piece is moved in a predetermined manner so that an accurate position of the test piece relative to the metal detection system is obtained.
Although the present method could be implemented while the article handling system is not operational, the metal test piece is moved along the flow path during normal operation of the article handling system. The advantage of this method is that typically, the articles themselves have some metallic qualities and therefore it is important that the metal detection system is not sensitive to the normal articles, but is still sensitive to the passage of rogue metal items. If the test is carried out in the absence of articles, then the metal detection system could be set at too sensitive a level. Of course, where the articles comprise (unwrapped) foodstuffs, it may be necessary to dispose of those articles which have passed along the flow path at the same time as the metal test piece. However, the advantage achieved by on-line monitoring exceeds this disadvantage.
The metal detector test system could be implemented in a number of different ways. For example, the test system may comprise a fluid operated cylinder coupled to a probe supporting the test piece, and a control system to control the supply of fluid to the cylinder to force the probe to move the test piece along the flow path. The cylinder could be pneumatically or hydraulically actuated.
In a second embodiment, the system comprises a linkage assembly comprising a number of links, pivoted together in a concertina arrangement, the test piece being supported on one of the links; and a control system to extend the linkage assembly to move the test piece along the flow path.
In a third embodiment, particularly where the flow path extends in a substantially vertical direction, the test system comprises an elongate flexible line which can be lowered along the flow path to carry the test piece and a control system to control the payout of the line.
In some cases, the metal test piece could remain in the flow path when not in use, even though it may contact the articles being handled. However, in many cases, this is undesirable and therefore preferably the metal detection test system is operable to move the test piece to a retracted position where it does not interfere with articles flowing along the flow path. In the case of a vertical flow path, this can be achieved by retracting the metal test piece to a position upstream of the point at which articles enter the flow path.
Typically, the parts of the metal detection test system which can be brought into the vicinity of the metal detection system are non-magnetic. This minimizes the risk that items other than the metal test piece are used to adjust the sensitivity of the metal detection system.
In general, the article handling system has a single metal detector test system. However, in some cases, more than one such system of either the same or different construction is provided. This enables the metal detector to be tested under different conditions without having to replace the test piece. For example, test pieces of different materials (iron, stainless steel, etc.) or different sizes could be provided on the different test systems.
The present invention is applicable to a wide variety of article handling systems, but is particularly suitable for use with weighing machines, and most particularly in combinational weighing apparatuses.